So I was playing on my amp yesterday and it all of the sudden started making this spurting, crackling sound and it was very loud. My amp is a Marshall JCM 600. It is a 60 watt tube amp. I just recently had some work done on it and it cost me $174, so as you can imagine, I am very scared. I tested to make sure it wasn't the cables or my guitar and it is neither of them. I have also tested to see how it works with different gain levels and there is not much of a difference between clean and dirty. The crackling will start after I've been playing for about 5 minutes and continue as long as I'm picking or touching the end of the cable. If I put the amp on standby or turn it off, then back on again, it will go for another 5 minutes without making the noise.
Sounds more like a grounding issue to me or possibly a microphonic preamp tube. However, it could be something more serious, like a bad capacitor(s).

What did your amp tech do?

I would take it back to them first and foremost.
The amp tech replaced all of the fuses and I believe he replaced the power tubes. He also did a few other really technical things that I can't remember
Quote by JMadd14
The amp tech replaced all of the fuses and I believe he replaced the power tubes. He also did a few other really technical things that I can't remember


I think you got really technically screwed over.

Replacing fuses and tubes is nothing. Easy peasy. I'd take it back there and demand satisfaction. Put your foot down. Show them this thread. Unless there is something I'm not aware of you got royally screwed over.

Did you take it in because it had a problem?
Do you have any spare preamp tubes? Switch it in 1 at a time. It sounds like one crapped out.

It even could be a power tube. Do you know which tubes he replaced?


Before anyone needs to go crazy tubes can die at any time. You would hope to not have a brand new one die but it does happen. Just make sure the power tubes aren't glowing bright red. If they are shut it off and take it in. If they aren't glowing red then you probably won't damage anything (Heaters will glow when the amp is turned on)

I had a brand new preamp make the same noise you are describing after about 4-5 minutes. It had never been used before. I could tap on it and get it to stop making the noise.

And you should always have at least 1 spare preamp. If not shame on you
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Last edited by R45VT at Jan 27, 2014,
Turn the lights off in the room and check out
how your power tubes are glowing if one or
more is flickering or fading in and out that'd be
the problem. One of my amps did this last week
and was making nasty feedback popping noise
and sounded like crap even with no guitar plugged
in did this only when off stand by and started after
I'd play a bit. Check it out. But I'd take it back to
tech and demand some form of recourse.
The reason I took the amp in in the first place was because it made a sound similar to what I'm hearing now and then got really quiet. I turned it off then back on and no sound came through. That's when I took it in to the tech.
I'd just take it back for what you
were charged it should be in proper